Project Summary/Abstract Clinical practice guidelines for preservation of the upper limb following spinal cord injury (SCI) are a promising tool for adults with SCI. Yet, adult manual wheelchair users following these recommendations for stroke patterns and movement strategies still have up to 84% occurrence of shoulder pain. Furthermore, as this is the only recommendation for standard of care of individuals with SCI it is currently being applied to children with SCI without sufficient evidence of effectiveness throughout the lifespan. Our long-term objective is to establish the desperately needed clinical practice guidelines for children with SCI while at the same time improving those for adults. We know that children are not just small adults due to ongoing musculoskeletal development and a maturing brain. Patient specific rehabilitation strategies, that incorporate consideration for the age of the patient at onset of injury, are warranted throughout the lifespan. Our group has found that adults with pediatric onset SCI have less shoulder pain than those with adult onset SCI, despite more years of wheelchair use. Furthermore, we have evidence that children with SCI have less pain and higher variability of movement than adults in regards to stroke patterns, shoulder joint forces, and shoulder joint moments during manual wheelchair mobility. However, we do not definitively understand why children and adults with pediatric-onset SCI have a lower incidence of secondary medical conditions, specifically pain and presumably pathology. Based on our preliminary studies, we have a compelling reason to believe that variability of propulsion stroke patterns and joint dynamics play a key role. This allows us to hypothesize that movement variability of manual wheelchair propulsion is significantly greater in persons with pediatric-onset SCI than adult-onset SCI, which ultimately reduces cumulative shoulder joint demands, shoulder pain, and progressive pathology. We propose to test this hypothesis by quantifying glenohumeral joint dynamics, pain, and pathology, using motion analysis with advanced biomechanical modeling, outcomes measures, and ultrasound imaging, respectively. We will then determine the effects of age of onset and variability on the underlying rotator cuff and bony forces using personalized musculoskeletal simulations. We expect to find an effect of age of onset of SCI on shoulder joint dynamics and stroke patterns with shoulder pain and pathology manifesting with decreased movement variability (overuse). The results of these studies are essential for creating innovative rehabilitation strategies to alleviate shoulder pain and pathology in manual wheelchair users with SCI. These paradigms are crucial for preventing pain and subsequent shoulder disease such as tendinopathy, early onset arthritis, and degenerative joint disease.